[PATCH] fix oops in scsi_run_queue()

[James Bottomley <James.Bottomley@suse.de>]

The recent commit closing the race window in device teardown:

commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
Author: James Bottomley <James.Bottomley@suse.de>
Date:   Fri Apr 22 10:39:59 2011 -0500

    [SCSI] put stricter guards on queue dead checks

is causing a potential NULL deref in scsi_run_queue() because the
q->queuedata may already be NULL by the time this function is called.
Since we shouldn't be running a queue that is being torn down, simply
add a NULL check in scsi_run_queue() to forestall this.

Signed-off-by: James Bottomley <James.Bottomley@suse.de>

---

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9901b8..03979f4 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -404,6 +404,10 @@ static void scsi_run_queue(struct request_queue *q)
 	LIST_HEAD(starved_list);
 	unsigned long flags;
 
+	/* if the device is dead, sdev will be NULL, so no queue to run */
+	if (!sdev)
+		return;
+
 	if (scsi_target(sdev)->single_lun)
 		scsi_single_lun_run(sdev);